The present invention relates to a radar system and to associated apparatus and methods. The invention has particular although not exclusive relevance to the application of new capabilities of persistent radar technology to enhance several aspects of wide area surveillance and achieve new services and new service features within a Field of Surveillance.
The technological background to the present invention lies in the so-called ‘Holographic’™ radar technology disclosed in the International Patent Application having publication number WO2008/145993 and the International Patent Application having publication number WO2009/144435. In these applications a so called Holographic radar system was disclosed in which persistent illumination (without interruption by electronic or mechanical scanning) of a volume of interest, by a monostatic array, was beneficially used to allow accurate and reliable discrimination between targets of interest such as aircraft or the like and clutter having moving (and in particular rotating) parts.
Key to a particularly successful application of the Holographic radar system was the realisation that a practical radar system could be implemented in which the radar was deliberately constrained to operate substantially within the so-called Holographic limit, within which both the range and the range-rate of targets of interest would generally be inherently unambiguous. This contrasted with the prevailing view, at the time, that some form of inherent ambiguity, in at least one of range and range rate, was always necessary in any practical radar system because of the trade-off between unambiguous range and unambiguous range rate. Specifically, it was believed that in a radar system designed to have a sufficiently high pulse repetition frequency to determine range rate of a fast moving target unambiguously the coverage area represented by that unambiguous range would be impractically small and vice versa. Accordingly, much work in the art was directed at resolving such ambiguities in range and/or range rate from the inherently ambiguous target data.
Following the UK Government's involvement in a Spectrum Release Programme to release parts of the reserved communication spectrum for use by other users and related investigations into possible reductions in spectrum occupancy by primary surveillance radar used for air traffic control purposes a further development of the radar technology was proposed. Specifically, in response to the general need for radar technology which allows the spectrum used by existing primary surveillance radar (typically in the so called ‘S’ band—2 GHz to 4 GHz) to be released, without materially reducing air surveillance capability, a multi-static radar system was proposed in which persistent illumination of a volume of interest was used beneficially, without the same requirement to operate inherently ambiguously, to provide a low bandwidth solution whilst, at the same time providing significant improvements in surveillance performance. This technology was described in the application from which this application claims priority.
In the multi-static radar system for providing surveillance, the radar system included a plurality of radar receivers and a plurality of radar transmitters arranged in a multi-static configuration to form at least one radar cell to provide an area of radar coverage within that cell. Each of the radar transmitters was a static transmitter that persistently illuminated a respective radar cell with a radar signal and that was synchronised or controlled as a part of the radar system. Each radar receiver was a static receiver operable to receive radar signals from within a respective radar cell, including radar return signals echoed from any object as a result of illumination by one or more corresponding radar transmitters. The respective radar signals received at each radar receiver were then processed to determine information relating to the position of a detected object and/or the motion of that object.
The inventors have realised more recently that the underlying feature of persistent illumination has a significantly further reaching than previously considered. In more detail the inventors have conceived of a number of new applications that have become enabled by use of persistent illumination in radar technology and have conceived a number of significant improvements to existing radar applications, beyond that currently believed possible with such technology.